What I want to address with this post is the process of obtaining the public key and thumbprint of the certificate used for encryption. A lot of examples I’ve seen are following the basic concept of retrieving the certificate from the local server where the mof will be deployed, but that requires firewall openings to all servers and credentials to them, and I think this might be a better/simpler alternative to that, at least in some cases.

So I’ve written a function (link at the bottom of this post) that gets the information needed straight from a Microsoft Certificate Authority (aka Active Directory Certificate Services) instead of all the different servers, which I think simplifies the process a bit.

I’ve also added some other properties to the returned objects to make it possible to use this advanced function for monitoring expiring certificates.

I’ll give you some examples on how to use this function below!

I’d also like to point out that I found a lot of parts of this code on the internet, I’ve just added a few extra things to it and wrapped it in an advanced function. I’m not sure who is the original author of this code though, if anyone knows, please add a comment below so I can give credit where credit is due! Thanks to whoever you are! 🙂

So, the process itself is pretty straight forward, specify your CA instance and what certificates you are interested in and the function will return them for you. You could for example do this:

When deploying SCOM (System Center Operations Manager) in a multi-forest environment, you use certificates to establish the trust between the servers. Since we have CA Servers in every domain, we started up with configuring autoenrollment for all the SCOM Gateway Servers, and made sure all the different CA servers were added to the trust-store of the central servers. (I will not go through that process now, if you want me to, leave a comment).

So autoenrollment now works, but that isn’t really enough, is it? We still need to configure the Gateway Server to actually switch to the new certificate when it arrives.

The tool Microsoft has given to us to do this is MOMCertImport.exe, but that tool gives you a pop-up that you actually need to click on… Not very “automatable”.

After some research, we could find that all this tool seems to do is to add the certificates serial number, backwards (in pairs), as a binary key in the registry. That is very automatable! 🙂

Before you start, you should know that this method is probably NOT supported by Microsoft, on the other hand, if it fails, you could run MOMCertImport.exe and see if that helps…

A code walkthrough follows:

Let’s start with setting up some user controlled variables, like what Certificate Template is used and where the registry key is located:

It’s now time for some regex-magic again, we want to pair this number up (2 and 2), and then reverse those pairs. I must confess I did a couple of rewrites of this before I found one that seems quite effective:

# Reverse the serial number to match the format in the registry
$ReversedPairs=[regex]::Matches($SerialNumber,'..','RightToLeft') | ForEach-Object { $_.Value }

The two dots (‘..’) tells powershell to group them, and the ‘RightToLeft’ reverses them. The last foreach is to get only the values and nothing else.
But it needed to be in binary format aswell, we achieve that by doing this: